Method of manufacturing colloidal inorganic oxide aquasols



Patented Nov. 6, 1951 UNITED STATES PATENT OFFICE 2 2,573,743 I iinrnon or: 'Am a ACTUR ING coiinoimi. INORGANIC OXIDEAQUASOLS Henry S.- Trail-,- Qiii'ncy, Mass, assignor to Mon saiito Chemical Company, St. Louis, Mo., a corporation of Delaware No Drawing. Application Jul 31, 1948, a Serial No. 41,892

Claims. (01. 252-313) "rue present invention rent-es to improvements in'the preparation of inoi anic oxide aquasols, anditmore particularly relates to improvements the manufacture of concentrated silica aquasels.

It has been proposed -heretofore to repare I silica aquasols by passing a dilute aqueous sodium silicat'e:solutioncomprising about 3% S102 through ion-exchange zeolites which have been prepared by treating a carbonaceous material such as brown coal-and the like with concentrated sulfuric acid. The silica aquasol which is obtained as the eiil'uent from the zeolite comprises about3% silica and istoo" dilute to be commencialliy useful as produced.- Attempts to prepare more highly concentrated silica aquasols directly byuseof ion exchangematerials have not been successful heretofore becauseof gel formation in the ion-exchange bedwhena more highly con ceutrated solution of sodium silicate is employed. Ithas been necessary; therefore, .to concentrate the dilute silica aquasols prepared by the above concentrated silica aquasol by the use of cationexchange materials, but also provides a silica aquasol which comprisescolloidal silica having a relatively large particle size. 'Ifhe silica aquasol produced by the method described herein is par tieularly useful when applied to cotton and wool fibers prior to spinning since it increases thestrength of the spun yarn and facilitates the spinning of finer yarnsthan are ordinarily ob'-,

. some by sp n countered Yams One object of the presentinvention isthapreparation of inorganic oxide aquasolsi-rom morg arnczox-ide compounds with the aidof cation-ex-- change materials by an improved and eflicient process.

' A further object oiithe present invention the preparation of concentrated silica aquasols 'from. alkali metal silicates with the aid 5 of cationex*--' change. materials by a substantially continuous method. c

A further obiect ,of the present invention the preparation of silica aquasols having-colloidal silica particles of substantially larger :size than. those normally obtained by the use rot cation-exchange methods;

Still further objects and advantages of the present invention will appear from the following description and the appended claims.

For convenience in description the. presentinvention is described with reference to the preparation of silica aqua'sols. However, it is to be understood that the method and-principles de= scribed hereinafter may also be applied 'to'the preparation of aqueous colloidal solutions of tungstic acid, vanadium oxide, molybdenum trioxide and other inorganic oxides as will be ape: parent to those skilled in the art.

of primary importance in thepractice of the present invention is the instant discovery that alkaline reacting silica aquasols comprising up to, 30 by weight or more of colloidal silica toeg'ether with a small proportion of ionic silica say about from: 1 to 4% by weight based on the total water present in the mixture can be passed through a bed of cation-exchange material or resin without appreciable gel formationeither in the exchange bed or in the efliuent issuingtherefrom. The principal limiting factor on the con.- centratlon of the silica aquasol which can be passed through an exchange bed in this manner is the viscosity of .the aquasol. In addition, it has presently been found that when the 'eflluentf'rom the above mixture is alkalized or made alkaline reacting with a small proportion of an alkaline or basic compound capable of ionizing to iorm' alkali metal, ammonium or quaternary ammo-v nium ions and the alkalized efliuent is then heat treated at a temperature essentially above C. for a period of time sufiicientto convert the ionic silica contained therein to colloidal silica, an ad ditional small proportion of ionic silica can be added thereto and passed through a bed of fresh or acid regenerated cation-exchange material without appreciable gel formation in the ex-, change bed. By application of the foregoing principles concentrated colloidal silica 'aquasols are continuously prepared as hereinafter "described the use of ion-exchange .materials.

The term ionic silica as employed hereinis' intended to mean silica whichis chemically com: bined with an alkali metal such as sodium, but is capable of being ionized in aqueous solution'or silica which has an average particle size below about 40 mu as determined by super-centrifug ng. techniques. The latter type of silica does mitl 6,6 settle out of solution when the-solution is super-+1 3. centrifuged at a centrifugal force equivalent to 62,000 times the force of gravity.

As examples of alkaline or basic compounds which are employed to alkalize the efiluent in the manner described above may be mentioned ammonia, ammonium hydroxide, sodium hydroxide,

sodium silicate, potassium silicate, benzyl tri-- ethyl ammonium hydroxide, tetramethyl ammocarry out ,the heattreatme nium hydroxide and the like. Of these ammonia,; I

ammonium hydroxide and the alkali metal sill: cates are preferred.

When the above described principles are employed in carrying out the present invention, H

10. i size. This is accomplished in general by carry- ""i'ng "out-the "heat treatment of the eflluent at as concentrated silica aquasolsv containing up to 30% or more colloidal silica can be prepared from silica aquasols containing only about 3% by Weight of colloidal silica by continuously r'e-' cycling the alkalized and heat treated effluent through a cation-exchange bed together with a z small proportion of ionic silica. Likewise, the same process can be carried .out by starting with an aqueous solution of .ionic silica such as-sodium silicate, containing up to 4% of ionic silica. On the other hand, the processor.v method described herein can be initiated by passing a concentrated colloidal silica aquasol together with a small proportion of .ionic silica through a cation exchange bed anda small proportion of silica aquasol can be withdrawn from the efiiuent either prior to or afterthe heat treatment of the efiluent and the balance of the eflluentafter it has been alkalized and heat treated can be recycled through the exchange bed together with another small proportion of ionicsilica. Such concentrated colloidal silica aquasols may be prepared. for example, byrecycling a dilute silica aquasol as described above the build up the concentration, of silica therein} or by evaporating water from a dilute silica aquasol prepared by passing a sodium silicate solution through a bed of cation-exchange material and then. alkalizing and heat treating the concentrated silica aquasol .to convert the particles therein to the colloidal silica form. When operating according to the of the aquasol is effected;;--

The recycling ofefiluent'through the exchange bed after it has been heattreated and after a small proportionof ionic silica has been added thereto can be carried out almost indefinitely by repeating the above procedure depending to a considerable extent upon the conditions employed during the heat treatment of the efiluent. It is during this heat treatment that the ionic silica contained in the eflluent issuing from the exchange bed is converted to colloidalsilica and the efiluent becomes sufiicientlystable to be re cycled without appreciable gel formation therein. The conversion of ionic silicato colloidal silica is affected primarily by the temperature to which the eilluentis heated, the alkalinity of the efiluent: and the duration of heating. By increasing any or all of these factors, the rate of conversion of ionic silica to colloidal silica is increased.

However, these factors of temperature, alkalinityand. duration of heating also influence the ultilow;a temperature and with as little alkali metal,

ammoniumor squaternary ammonium ion as is practicable .for the conversion of ionic silica to colloidal silica. V r

I n apre'ferredembodiment of the invention an "alkaline reacting silica aquasol comprising from about-10 to 25% colloidal silica is admixed with an aqueous alkali metal 3 silicate solution preferably, an aqueous so dium silicate solution in an amount suflicient to, provide up to about, l%. and; preferably up, to 3% .by weight ,.o1. .ionic,silicaJ,

based onthe totahquantity o f waterpresent 'in. the final mixture. This mixture or feed stock jis;v

then run through abed of cation-exchange material which operates ,ona hydrogen regeneration.

cycle until the 1 alkali ;;metal,.silicate; begins: :120- break through the; bedv :wit-hout appreciable ad-, sorption of alkali metal ions, by,;-the: exchange material. At this point the pH of the total efllu-,.

efliuentis alkalized'b'y adding .thereto an amount. of alkaline compound sumcient to provide from about.0.05 .to 0.2% .by weight, .(based v.on."th-e total eflluent) of alkali metaL. ammonium. .or. -quater nary ammonium ions,.;.pref.erably sodium ionsderived-from sodium .silicate. -..This can be.ac-.

complished byitheadditionz-to the, effluent of feed stock obtained. from the :exchangebed after the break throughpoint reached, or the alkaline compoundaddition can be made separately afterthe total: quantity of effluent from the exchange bed hasbeen icollectedand is still slightly acidic orfhas a pH'slightly' below the neutral point.

The above eflluent'is'h'eated above about C. fora sufficient :period 'of'time td convert the ionic silica present ther'einLtothe colloidal silica form. In general, temperatures equivalent togauge steam pressures offrom about-60to- 200 pounds per square inch are suitable forcarrying out the heat treatmentof'jthe eliluent although higher or lower temperatures --may be employed depending upon the-alkalinity of the eflluent and the duration'of the heat treatment. At the above described steampressures and alkaline ion con centrations a' period'ofheating of about 10 to minutes has been found to be satisfactory forconverting ionic silica tofth'e colloidal form. The short heating period of 10 minutes 'corresponds to temperatures-equivalent to-"about 200 pounds'per' square'inch'gau'gesteam-pressure;

The present invention is preferably practiced" by recycling the heat treated 'eflliient after it-has been cooled'throug'h a bed of fresh or acid regenerated cation-exchange material togetherwith another proportion'of aqueous alkali metal silicate solutionso as" to provide up to about 4%. by weight of-ionicf -silica' in the manner hereinnt under 5 When :the foregoing process: is operated so: as to prepare a silica aquasol having a substantially fixedicolloidal silica concentration as,. ,for example, 18%, 20%, or colloidal silica concentration by weight, a proportion of thexeflluent substantially equal in weight to the amount of alkalimetal silicate solution. initially added is withdrawn at some stage of the recycling process and prior to the addition or furtherquantities of ionic silica. The portion withdrawn aftereach pass is collectedas a marketable productiif it has been heat treated as described or can be heat treated separately after it has been alka.-'- lized if it is withdrawn from theeflluent issuin from the exchange bed.

When inorganic oxide aquasols other than sllic'a aquaso'ls are prepared by a substantially similar process it is generally more diflicult to prepare colloidal solutions containing highconcentrations of inorganic oxide since sols such as tungstic acid sols, vanadium oxide sols and the like have a relatively short stable life even at low concentrations. However, it is possible to produce 1 such: sols in more highly concentrated form in accordance with the present invention and by the. use of cation-exchange materials than has been possible heretofore. Such sols may be prepared, .for example, from sodium tungstate, so-

dium vanadate, sodium molybdate and the like. Any suitable cation-exchange material which operates on a hydrogen regenerating cycle. and issubstantially stable to dilute alkaline and acid solutions may be employed in the practice of the present invention. Many types of inorganic, organic and synthetic type cation-exchange ma terials are available for use in carrying out the process described herein.. As examples of those which. are particularly suitable are the so-called synthetic types such as phenol-formaldehyde resins, tannin-formaldehyde resins and the like onderivatives thereof containing sulfonic or car- 'boxylic groups, or modified organic types such asbrown coal, peat and the like which have been sulfonated with concentrated sulfuric acid. .An' other particularly valuable cation-exchange material which is especially. suitable for userinathe practice of the present invention is polymerized divinyl. benzene containing nuclear sulfonic acid groups. Such cation-exchange materials canb'e employed for a large number of cycles without substantial loss of bed dimensions by simple regeneration with dilute' mineral acids such as hydrochloric acid, sulfuric acid and the like. 1

1. .The regeneration of cation-exchange material's mhichhave been exhausted by the adsorption of eations can be accomplished by well-known procedures heretofore described in the prior art.

"One such procedure is tofirst back wash the exe hausted-bed with Water so as to remove a large portion of the silica aquasol adhering to the bed. This is then followed by a regenerationtreat ment with a dilute mineral acid after which a substantial portion of the acid is washed out'of' the bed by back washing the bed with water. This procedure is only illustrative of those -employed in regenerating cation-exchange-materials'and other procedures may be used if desired. The regeneration of the exchange bed may be carriedout at any stage of the method hereinde-' scribed for the preparationof silica aquasols. In general, the regeneration of the exchange bedis started as soon as the total eliluent from the bed has been collected. When the regeneration oi} the bed is carried out expeditiously, it ispossibleto use the-same exchange bed therecy (all 6 cling process since regeneration can be effected while thesilicaaquasol eflluent from theprevious run is being heat treated.

A further understanding of the presentinvention will be obtained from the following examples which are intended to be illustrative, but vnot limitative of the scope of the invention, parts andpercentages. being by weight unless otherwise specified.

. Example I A concentrated silica aquasol was prepared by first allowing an aqueous sodium silicate solution (3.1 to 1 ratio of SiOa) containing about 3% ionic S102 to flow by gravity through a, 12 inch deepbed of acid regenerated cation-exchange material contained in a cylindrical glass tube having an internal diameter of approximately 17/,- inches. The rate of flow was about 300 pans of solution per minute. The silicate solution was allowedto flow through the bed until. the total effluent which was collected in a suitable tank; contained about 0.03% sodium ion. This eflluent was then concentrated by evaporating the water therefrom at a temperature of about C. until the silica concentration was about 20% and was then heat treated in an autoclave at a tempera ture equivalent to a gaugexsteam pressure of pounds per inch and for a period of 15 minutes. Three thousand parts of the above 20% silica aquasoi W'ie admixed. with 450 parts of an aldliolis sodium silicate solution 3.1 to 1 ratio of S105 to' NaO) comprising about 19.3% of ionic S102. The mixture was thenallowed to flow through a lation-exchange bed 12 inches in depth con'' tained in a cylindrical glass tube having an inter nal diameter of approximately 1% inches. The rate of flow through the bed was about 300 parts of mixture per minute.' The efliuent was collected in a suitable tank until the pH of the mixture was about 6.8 as measured by a Beckm'an pH meter at atem'perature of about 28 C. Additional quantities of the elfluent from the ex change bed were allowed to flow into the tank until the sodium ion concentration of the mix ture in the receiver was about 0.12%. The collction of enuent from the exchange bed was then discontinued. The collected efilu'ent was then heated in an autoclave at a temperature equivalent to pounds per inch gauge steam pressure for a period of approximately 25 min-'- utes. The heat treated effluent can be used as a commercial silica aquasol containing about 23% colloidal silica or it may be utilized in the manner described in the following example.

Example II Theheat treated effluent as obtained in Ex-' ample Iwas divided into two portions as followsf i Parts lfli A----,- 9 Efiluent B 3'000' exchange bedwas shut oh and no more efiiuent 7: was. collected. Sufficient quantities of theabove described sodium silicate solution were then added to the total efiluent until the sodium ion concentration ofthe mixture was about 0.05%. Four hundred and fifty parts of the eflluent were then withdrawn and the remainder "was heated in .an autoclave at. a temperature equivalent:.to.

120 pounds per .inch of gauge steam pressure for; a period of 60 minutes. This efiiuent; afterrcool-z' ing to about 30 0., was then ready to be recycled through the regenerated exchangebed after an addition thereto of more'ionic silica inflthemaiiener described above. f The 450'parts of effluent which had beenwithdrawn prior to heat treatment was thenheated' in an autoclave at a temperature equivalentto 200'poun'ds per'inch of gauge steam'pressure for a period of 30 minutes and after cooling-was ready for commercial use'.' This aquasol contained colloidal. silica having a'. large average particle size and was particularly effectivefor' increasing the strength'bf cotton yarns when applied to cotton'slive'rs prior to spinning; f The above procedure can be repeated as often as desired and providesa' continuous method of preparing silica aquasols.

Y Example HI therefrom at a temperature of about 100 C.

until the silica concentration was about 20% and was then heated in an autoclave at a temperaof was about 0.10%. The effluent was then heated in an autoclave at a temperature equivalent to 170 pounds per inch gauge steam pressure for a period of 20 minutes and was then allowed to, cool.

When the above heat treated efiluent is recycled in the manner described in Example-ll. the recycling can be carried out-almost indefi nitely without substantial gel formation in the exchange bed. I

Example IV I A concentrated colloidal silica aquasol wasprepared in the following manner: A dilute aqueous sodium silicate solution (3.4 to 1 ratio of $102 to NazO) containing about 4% ionic silica was allowed to flow by gravity at the rate of 275 parts per minute through a 12inch deep bed of acid regenerated cation-exchange material contained in a cylindrical glass tube having an internal diameter of 1% inches. The

8'; emuenfl-was collected in a suitable tank untilit contained about 0.06% sodium ion and 'thenthe collection of effluent was discontinued. Thisetfluent was then heated in an autoclave ame temperature equivalent to a gaugesteam pressure of .150 pounds per square inch for a. period of 10 minutes. The heat treated eflluent, which contained about 4% colloidal silica as aresu'ltof the heat treatmentunder alkaline conditions,; was'thencooled'to about 30 C. 1.. ,4; -,Two.lthousand parts of the cooled efliuent 'asobtained above; which contained about.i4% ..jco1:.- loidal silica, were admixed with 400 parts of aqueous sodium silicate solution (3.4170 1 ratio of SiOz to NazO) containing about23%*of ionic: silica and the. mixture was allowed to flowg'by gravity at-the rate of 300 parts a minute throughv the bed of'acid regenerated cation-exchange ma: terial. The efliuent was collected in a suitable tankv until it contained about 0.07% .of sodium ion and it was then heated in an autoclavetat :11 temperature equivalent to a gauge. steam-pres;- sure of pounds per square inch for a period of 15. minutes. The effluent was then cooledto. about 30 C.

Two thousand one hundred and fifty-fiveparts of such cooled efliuent were admixed with-425 parts of aqueous sodium silicate solution (3.4 toil: ratio of S102 to NazO) containing 19.3% of ionic silica and the mixture was allowed to flowlby gravity at the rate of 300 parts per -.minute through the bed of acid regenerated'cationiex-i change material; The effluent was collected a suitable tank until it'contained abouti0;05%;- sodium ion and was then heated in an autoclave at'atemperature equivalent to a gauge steam pressure of 100 pounds per square inch for a period of 12 minutes. The heated efiluent' was thencooled to a temperature of about 30 C. and contained about 8.5% colloidal silica. .5

By recycling the alkalized and heat treated effluent after it has been cooled together with a quantity of aqueous sodium silicate solution (3.4 to 1' ratio of SiOz to NazO) containing about 19.3% ionic silica, suflicient to provide about 3%- ionic silica based on thetotal water present in the mixture through the bed of acid regenerated cation-exchange material in the manner described above, a 20% colloidal silica aquasolwas readily obtained. Such colloidal silica aquasol 'canbe employed in place of the 20% colloidal'silica; aquasol initially employed in Examples I and III, or it may be used as a commercialcolloidal silica aquasol for the treatment of textile fibers prior tospinning, for coating papers andthe' like. The same bed of cation-exchange material was employed for each recycle of the efiiuent as-de scribed in this example. The bed was regenerated after each recycling operation by first back washing the bed'with large quantities of water, after which, a 4% hydrochloric acid solution was al-' lowed to flow by gravity through the bed until the acid issuing therefrom was substantially free from sodium chloride. The bed was washed down with water until the efiiuent had a pH of about 5; The cation-exchange material employed in the foregoing examples is a polymerized divinyl benzene containing nuclear substituted sulfonic acid groups. The particles in the exchange material are substantially spherical and have an average diameter varying between about 0.5 to 1.5mm. a 7

Although an autoclave is employed in dairy ing out the heat treatment of the alkalized silica aduasor em efit inah irsregoing examples other types f pparatus e; p'able of withstanding steam :"pres'sures above 100 "CQ may" be employed. "Thus heat" exchangers, tubular "heating devices' and other apparatus capable "of withstanding the "pressure generated-maybe used.- 1

' "Va'rious'modifications maybe made in the practice of the present invention as will be apparent "those sk'ille'd in the ar't. Various types of apparatus; for 'example," may be employed 'in taifl fying out the "method described -here'in depending {upon the quantity'of silica aquasol prohe employedto utilize "the heat values more efiicintly and heat retention units "may be employed to carrylout th'e heat treatment of the silicaaquasols-aftr the-{desired temperature-has ben' reached. The area'and depth of theexhlnge bed "andthe number of exchange beds "employed may also he varied considerably dey periding upon the amount of silicaaquasol promaterial until-thepH of the total efliuent is slightly belowthelneutral .point; alkalizing said efiluent withanalkaline compound capable of y ielding ions selected from th'e groupconsisting of alkali metal, ammonium and quaternary ammonium ions; *heating the'efiluentat a temperature and for a duration of time sufficient to convert'th'e ionic form of the inorganic oxide to col- Zloidal form and then recycling a portion of the .iefiluent together with a small proportion of a solution of the same inorganic oxide in ionic form through a bed of acid regenerated cation-exchange materialin'substantiallythe same manner.

=2. A method of preparing silica:aquasolswhich comprises passing a mixture of an alkaline reacting colloidal silica aquasol and a small proportion of a solution of ionic silica through a bed of cation-exchange material until the pH of the total effluent is slightly below the neutral point;

alkalizing said effluent with an alkaline compound capable of yielding ions selected from the group consisting of alkali metal, ammonium and quaternary ammonium ions; heating the efiiuent at a temperature and for a duration of time sufl'icient to convert the ionic silica to colloidal form and then recycling a portion of said eflluent together with a small proportion of a solution of ionic silica through a bed of acid regenerated cationexchange material in substantially the same manner.

3. A method of preparing silica aquasols which comprises passing a mixture of an alkaline reacting colloidal silica aquasol and a small proportion of a solution of ionic silica through a bed of cation-exchange material until the pH of the total eiiluent is slightly below the neutral point; alk-alizing said efliuent with an alkaline compound capable of yielding ions selected from the group consisting of alkali metal, ammonium and quaternary ammonium ions; heating the emue t at atemperature essentially above C. and for La duration of time sufficient to convert the ionic silica to colloidal form; regenerating said bed ot cation-exchange material after said e'filuent is removed therefrom and thenrecycling a portion of the eiiluent together with .a small portion of a solution of ionic 'silica through the bed of :re- -generated cation-exchange material insubstantially the same manner. 7.

4. A method of'preparing silica taquasolswhich comprises passing a mixture of an alkaline reacting colloidal silica aquasol and a quantity .of aqueous sodium silicatesolution in an-amount sufficient to provide up to about 4%?by weight of ionic silica based on the water presentiin the mixture througha bed of cation-exchange material until' the pH of the totaleflluent zisrslightly bel'ow "the neutral point; adding thereto-an amount 2 of alkaline :compound-wsuih'cient to provide'at least 0.05% byvwei'ghtbased on the total efflu'entof ions selected .from 'the-group consistring of alkali 'metal, ammonium and quaternary ammonium ions; heating the efliuent'at attemperature equivalent to a gauge steam pressureaof T about 60 to 200 poundsper square inch and for aperiod of time suflicient to convert the ionic silica therein to the colloidal form'and' then'recycling a portionof said eflluent together with a quantity of'aqueous sodium silicate solution sufiicient to'provide-up'to about 4% by-weight of ionic "silica based on the water presen'tin the recycle mixture througha bed ofacid regenerated ture through a bed of cation-exchange :material until the pH ofthe total "efiiuent is slightlybelow thene'utral point; adding thereto a quantity of a sodium 'base suffic'ient to provide from about-0.05 1to 0.2%'by weight of sodium ions based ton-lthe total "efiluent; heating the -efiluent at a tempera- :ture equivalent to .3, gauge steam pressure of- -60 to 200 pounds per 'square inch for a period c! itimee sufficient to convert the .ionic silica therein to the colloidal form and then recycling a: major portion -'of the -'eflluent together with a ,quantity of aqueous sodium silicate solution suflicient to provide up to about 3% ionic silica through a bed of acid regenerated cation-exchange material in substantially the same manner.

6. A method substantially according to claim 5 but further characterized in that the mixture of silica aquasol and aqueous sodium silicate solution is passed through the bed of cation-exchange material until the total efiluent comprises about 0.05 to 0.2% by weight of sodium ions.

7. A method of preparing concentrated silica aquasols which comprises passing a mixture of an alkaline reacting silica aquasol comprising about 10 to 25% by weight of colloidal silica and a quantity of aqueous sodium silicate solution sufiicient to provide up to 3% by weight of ionic silica based on the water present in the mixture through a bed of cation-exchange material until the pH of the total eflluent is slightly below the neutral point; adding thereto a quantity of sodium base suflicient to provide about 0.05 to 0.2% sodium ions based on the total eiliuent; heating said efliuent at a temperature equivalent to a gauge steam pressure of about 60 to 200 :abvaua 11 pounds per square inch fora period of 10 to-120 :minutes and .then recycling the total efiiuent "minus a portion thereof substantially equal'in 'weight to the quantity of aqueous sodium silicate solution employed together with a quantity of q'uantity of aqueous sodium silicate solution suf-;

ficient to' provide up to 3% by weight of ionic silica based on'the water present in' the mixture :through a bed of cation-exchange material until the pH of the total effluent is slightly below the 7 neutral point; alkali'zi'ng said efliuent with aquantity of ammonium base sufficient to provide about 10.05 to 0.2% ammonium ions based on the total -eflluent; heating said'eiiluent at a temperature equivalent to a gauge steam pressure of about 60 to 200 pounds per square inch for a period of,

about 10 to 120 minutes and then recycling'the total effluent minus a portion thereof substantially equal in weight to the quantity of aqueous sodium silicate employed, together with 'a' quantity'of aqueous sodium silicate solution suificient "to provideup to 3% by weight of ionic silica based on the water present in the mixture through a bed of acid regeneratedcation-exchange material in substantially the same manner. .6

A method of'preparing concentrated silica -aquasolswhich'comprises' passing a mixture of 'an alkaline reacting silica aquasol comprising about 10 to by weight of colloidal silica and a quantity of aqueous sodium silicate solution sufiicient to'provide up to 3% by weight of ionic silica based on the water present in' the mixture through a bedof cation-exchange material until the pH of the total eiiluent is slightly below the neutral point; alkalizing said efliuent with a quantity of quaternary ammonium base 'suflicient to provide about 0.05 to 0.2%quaternary ammonium ions based on the total'efiluentfheating said lefiluent at a temperature equivalent to a "gauge steam pressure of about 60 to 100 pounds per square inch for a period of 10 to 120 minutes and then recycling the total efliuent'minus a portion thereof substantially equal in weight to the quantity of aqueous sodium silicate employed, together with a quantity of aqueous sodium silicate solution suflicient to provide up to 3% by weight of ionic silica based on the water present in the mixture through abed of acid regenerated cation-exchange material in substantially the same manner.

10. A method of preparing silica aquasols which comprises passing a mixture of. an alkaline reacting colloidal silica aquasol and a quantity of aqueous sodium silicate solution in. an amount sumcient to provide up to about 4% by weight of ionic silica based on the water present in the mixture through a bed of cation-exchange material until the pH of the total ellluent is slightly below the neutral point; adding thereto an amount of sodium base suflicient to provide at least 0.05% by weight based on the total eflluent of sodium ions; heating the eflluent at a temper- .ature equivalent to a gauge steam pressure 01' about to 200 pounds per square inch and for a period of time sufficient to convert the ionic silica therein to the colloidal form without the formation of extremely large colloidal silica particles which tend toform a fioc in said bed off 7 cation-exchangematerial and then recycling a 7 portion of said efiluent together with a quantity of aqueous sodium silicate solution sufiicient to provide up to about 4% by weight of ionic silica based on the water present-in the 'recyclepmix ture through a bed of acid regenerated cationexchange' material in substantially the same manner. 7 HENRY S. TRAIL. i

REFERENCES CITED The following references areof record in the file of this patent:

UNITED STATES PATENTS Switzerland Dec. 17, 1923 

1. A METHOD OF PREPARING INORGANIC OXIDE AQUASOLS WHICH COMPRISES PASSING A MIXTURE OF A COLLOIDAL INORGANIC OXIDE ALKALINE AQUASOL AND A SMALL PROPORTION OF A SOLUTION OF THE SAME INORGANIC OXIDE WHICH IS PRESENT IN THE MIXTURE IN IONIC FROM THROUGH A BED OF CATION-EXCHANGE MATERIAL UNTIL THE PH OF THE TOTAL EFFUENT IS SLIGHTLY BELOW THE NEUTRAL POINT; ALKALIZING SAID EFFLUENT WITH AN ALKALINE COMPOUND CAPABLE OF YIELDING IONS SELECTED FROM THE GROUP CONSISTING OF ALKALI METAL, AMMONIUM AND QUATERNARY AMMONIUM IONS; HEATING THE EFFLUENT AT A TEMPERATURE TURE AND FOR A DURATING OF TIME SUFFIEIENT TO CONVERT THE IONIC FORM OF THE INORGANIC OXIDE TO COLLOIDAL FORM AND THEN RECYCLING A PROTION OF THE EFFLUENT TOGETHER WITH A SMALL PROPORTION OF A SOLUTIONOF THE SAME INORGANIC OXIDE IN IONIC FORM THROUGH A BED OF ACID REGENERATED CATION-EXCHANGE MATERIAL IN SUBSTANTIALLY THE SAME MANNER. 